Typically, fuel vapors are generated inside of the fuel tank due to temperature and fuel movement and are stored in a charcoal canister to prevent evaporative emissions of hydrocarbons into the atmosphere. These vapors are periodically purged out of the canister and sent to the engine where they are consumed during the normal combustion process. On a standard gasoline engine vehicle this can occur whenever required to prevent the canister from becoming stuffed and bleeding hydrocarbons into the environment. However, this cannot occur on a hybrid vehicle when it is operating in electric mode. A “plug in hybrid” vehicle may go many driving cycles without ever running the gasoline engine. Therefore, there becomes a need for the fuel system to contain vapor for long periods of time by keeping the system sealed and under pressure in order to limit fuel evaporation. At elevated temperatures, the pressure build inside of the tank will be substantially higher than a conventional fuel system.
Currently, some solutions have been provided to the problem, which are namely:    1. To replace the current polymer tank with a steel equivalent capable of holding the pressure.    2. To optimize the tank shape for instance by providing tack-offs (also called “kiss points”), where during the molding of the tank, the top and bottom are dimpled to create a mechanical link between the two.    3. To use (generally metallic) straps as reinforcement.    4. To mold or mechanically lock into the tank surface, structural ribs which create additional rigidity.    5. To use a plastic bladder inside of a steel tank to control vapor generation and associated pressure.
However, each of these solutions has at least one drawback:    1. A metallic tank has a significant weight penalty over a polymer tank based on the properties of material density. The density of steel is ˜8 times higher than that of HDPE while conventionally tank walls are only 3-4 times thicker than steel tank equivalents. It is also cost prohibitive to make a small volume of steel tanks, due to the high cost of the stamping dies. The alternative is to make the conventional vehicle volume in steel as well, resulting in a potential degradation in corporate average fuel economy that offsets the gains made by the small volume of plug-in hybrids.    2. Shape optimization can only add so much additional pressure resistance while maintaining the properties required by the vehicle manufacturer. Tack-offs for example use a significant amount of available volume in the tank due to their inherent shape. They also reduce the impact resistance of the tanks And most of the time, they will not by themselves provide the required pressure resistance.    3. Strap reinforcement can be achieved but it can be difficult to manage as the underbody of a vehicle has complex shapes, and clearances to the underbody and ground are strictly enforced by the manufacturer. In addition, as straps are added, the additional weight of the straps begins to negate the weight savings of the polymer tank. Additionally, as the straps are generally not laminated to the tank surface, they do not offer significant structural advantages.    4. Solutions that are molded or mechanically locked to the tank surface are generally inserted prior to cooling of the tank, resulting in molded in stresses in the tank shell that could be detrimental to the performance of the tank shell.    5. Integration of the flexible bladders has been industrialized for conventional plastic tanks, however such technology has been abandoned, due the problem of fixing and sealing the bladder inside of the tank.